Method of forming centrifugal blower wheel

ABSTRACT

Disclosed is a centrifugal blower wheel including an end plate and blades extending from it. The wheel is given a conical configuration by inserting a tool having circular periphery into the cylindrical space defined by the inner side margins of the blades. The tool is moved toward the end plate, forcing the blades to flare outwardly and placing them under bending stress. This blade stress tends to be relieved by centrifugal force acting on the blades during operating rotation of the wheel.

May 21, 1914 J. A. WOODEN METHOD OF FORMING CENTRIFUGAL BLOWER WHEEL Filed Aug. 21, 1972 Fig.3

United States Patent Office 3,811,978 Patented May 21, 1974 US. Cl. 156-160 2 Claims ABSTRACT OF THE DISCLOSURE Disclosed is a centrifugal blower Wheel including an end plate and blades extending from it. The wheel is given a conical configuration by inserting a tool having a circular periphery into the cylindrical space defined by the inner side margins of the blades. The tool is moved toward the end plate, forcing the blades to flare outwardly and placing them under bending stress. This blade stress tends to be relieved by centrifugal force acting on the blades during operating rotation of the wheel.

BACKGROUND OF THE INVENTION The advantages inherent in conically-shaped, centrifugal blower wheels are known in the prior art. Among these are lower inlet velocity for a given air moving capacity, increased effective blade area for a given lateral wheel width, and decreased losses due to air circulation at the end ring. The concept of the present invention particularly envisages forming a conical blower wheel by integrally molding, from a suitable plastic material, an end plate and blades by conventional means. At the conclusion of the molding operation the end plate and blades form a generally cylindrical configuration with the blades extending from one face of the end plate. An end ring is subsequently secured to the blade ends confirming the cylindrical shape of the assembly.

In forming the prestressed conical wheel of the present invention, however, prior to installation of the end ring, a tool having a circular peripheral surface is introduced into the cylindrical space defined by the inner side margins of the blades and advanced toward the endplate. Because the peripheral tool surface has a diameter greater than the diameter of the cylindrical space, the blades are flared outwardly a slight amount and placed under bending stress. Before the tool is removed, an end ring, having an outside diameter somewhat larger than the diameter of the endplate, is secured to the ends of the blades. The tool is then withdrawn from the assembly and the resulting structure is a conically shaped blower wheel having prestressed blades, the blade stress being relieved by the action of centrifugal force on the blades when the wheel is in operation. Further, the compressive stress under which the blades are placed when the assembly is completed results in a force tending to resist the bursting or outwardly explosive centrifugal force acting on the end ring as the wheel rotates at high speed. The conical wheel assembly, produced by the method described, can be economically tooled and production of the wheels has flexibility in that various wheel widths can be produced with minimum tooling change.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view of the blower Wheel of the present invention at an intermediate stage in its fabrication.

FIG. 2 is a side sectional view of the blower wheel of FIG. 1 at a further stage of its fabrication.

FIG. 3 is a fragmentary, front view, with a portion broken away, illustrating the completed conical blower wheel of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring initially to FIG. 1 there is shown a centrifugal blower wheel 10, having a generally concavo-convex, or dished, configuration, and carrying a hub 11 defining an axis of rotation for the wheel. Extending rigidly from the convex face of the endplate and arranged in a spaced, circular pattern about the marginal area of the end plate are blades 12 having ends notched as indicated at 12a. As previously mentioned, the endplate and blades may be integrally molded from a suitable plastic material. It will be noted that, as shown in FIG. 1, the endplate and the inner side margins of the blades define a generally cylindrically shaped space and, if a conventional blower wheel were to be formed from the structure shown in FIG. 1, only an end ring, having the same outside diameter as the endplate 10, would be added, the end ring extending around the notched ends 12a of the blades and giving rigidity to the assembly.

In forming the conical blower wheel of the present invention, however, as may be seen in FIG. 2 prior to installation of an end ring, the endplate and blades are held in a suitable fixture (not shown) and a tool 21, having a circular peripheral surface 22 is introduced into the cylindrical space defined by the blades 12. The surface 22 may be tapered somewhat, as shown in FIG. 2, to facilitate entry of the tool into engagement with the inner side margins of the blades. A central portion of the tool 21a slides within the hub 11 and insures that, as the tool is advanced from the end of the assembly to its position of FIG. 2, the center of the circular, peripheral surface 22 will advance along the rotational axis of the wheel as defined by hub 11.

As the tool surface 22 is advanced to its position of FIG. 2, the blades 12 will be flared outwardly. The flaring outwardly of the blade ends by the tool surface 22 generates a restoring force acting radially inwardly at the blade ends 12a, as indicated by arrow 31 in FIG. 2. With the tool surface 22 in place as shown in FIG. 2, an end ring 30 is placed on the blade ends 12a and is preferably secured to the blades by solvent bonding to form a rigid joint. The tool 21 is then backed from the assembly along the path indicated by broken line 32 in FIG. 2. The blades remain under some compressive stress which tends to be relieved by the centrifugal force (acting radially outwardly) on the blades produced when the wheel is rotated at operating speed about its axis of rotation. The restoring force indicated by arrow 31 in FIG. 2 also tends to balance or act against the bursting, outwardly directed centrifugal force exerted on end ring 30, the assembly is thus strengthened for operation at high rotational speeds.

I claim:

1.- A method of forming a conical blower wheel of the type having an endplate carrying a central hub and spaced parallel blades arranged in a circular pattern extending from one face of the end plate, said method comprising: introducing a tool having a circular periphery into the cylindrically-shaped space defined by the inner margins of said blades, the periphery of said tool having a diameter larger than that of said cylindrically-shaped space, then advancing said tool toward the endplate to thereby cause 2,991,004 7/1961 Denbo et a1. 416241 UX said blades to flair outwardly and to place them under 3,136,035 6/1964 Goettl 29-1568 bending stress, subsequently securing a unitary end ring 3,536,416 10/1970 Glucksman 416-178 to the outer ends of said blades to hold them in flared 3,635,588 1/1972 Lester 416-187 stressed position, and finally removing said tool from en- 5 3,692,428 9/1972 Bubb et a1 416187 gagernent with said blades.

2. A method as claimed in claim 1 including the addi- FOREIGN PATENTS tional step of inserting a portion of said tool into the cen- 1,079,271 4/ 1960 Germany 416241 A tral hub carried by the endplate to assure that the center 7,5 961 Italy 416-187 of said tool periphery moves along the rotational axis 10 of said hub as said tool is advanced. WILLIAM POWELL, Pnmary Examlller B. LLEIITE References Cited N Assistant Examiner UNITED STATES PATENTS 4 US. 01. X.R. 589,946 9/1897 Grunow 416-187UX 15 16-187 1,892,930 1/1933 Burman 416187 

